The article focuses on the discrepancies between the rules of the 1997 Polish Constitution and political practice. The main thesis is that the divergence is a result of the enduring effect of informal rules or institutions which emerged in the early period of Polish transition. The informal institutions are defined, following O'Donnell and Lauth, as stable rules that are created, communicated and executed outside formally sanctioned channels. This means that they are viable rules (i.e. they are perceived as a binding standard of behaviour) only due to dispersed, societally (non-state) administered sanctions. In order to clarify how informal institutions may dominate constitutional rules four institutions are examined: the Presidency and its inherent conflict with the Government, a degenerated form of the constructive no-confidence vote that stabilizes but weakens Polish governments, futile attempts to install a professional, non-partisan civil service, and a radical undermining of the non-majoritarian logics of the National Broadcasting Council operation. The conclusion is that a continuous domination of informal institutions may be proved despite a wide consensus among legal scholars arguing a new post-1997 era of stable constitutional rules as opposed to insecure patchwork constitution of the early 1990's. This has important consequences for Polish constitutionalism as its promise of stability and security of legal frame of reference is constantly challenged by the strength of informal institutions.